Photochromism of 2-Chloro-N-salicylideneaniline in Amorphous Polymer Solids

Abstract

Photochromism of 2-chloro-N-salicylideneaniline, Sa(H,2-Cl), molecularly dispersed in amorphous polymer matrices was investigated under conventional steady-state irradiation. The final conversion of photochromic reaction in amorphous polymers was found to decrease with temperature due to notable influence on a thermal back reaction. The effect of polymer matrix on the thermal decay reaction was explained by the half-life (1/t1/2) of the colored species and concept of free volume of polymer matrices: the values at 20°C for Sa(H,2-C1) in poly(methyl methacrylate) (PMMA), polystyrene (PS), and polycarbonate (PC) were 11.1, 3.0, and 2.5 min, respectively. This indicates that the size of free volume of PMMA is the smallest in the three polymers at room temperature. Arrhenius plots of 1/t1/2 for PC and PS broke obviously at 20 and 14°C in contrast to a linear relationship for PMMA, and apparent activation energies for the thermal decay reactions in both polymers were approximately half above the break points.